A control apparatus that converts DC voltage to AC voltage by a power converter and performs drive control for an AC rotary machine is generally used. In general, in order to drive the AC rotary machine with high efficiency, such a control apparatus for an AC rotary machine controls the torque by controlling the current of the AC rotary machine in accordance with sine wave PWM (Pulse Width Modulation) control based on vector control.
On the other hand, in the case where the AC rotary machine is driven with a relatively high frequency, it is necessary to maximize the electric motor drive voltage based on the DC voltage, and a drive method using a square wave voltage having a constant peak value is employed. In the square wave driving, the peak value of the voltage waveform based on switching control is constant, and the torque caused by the electric motor can be operated by operating the phase of the voltage waveform. For example, in the case of a permanent magnet synchronous electric motor, the torque can be operated by operating the voltage waveform phase relative to the rotor position.
However, the torque caused by the AC rotary machine varies along with the variation in parameters of the AC rotary machine (for example, in the case of a permanent magnet synchronous electric motor, the parameters are permanent magnet magnetic flux, inductance, and armature resistance). For example, if inductance is reduced by magnetic saturation due to applying the current to the AC rotary machine or if demagnetization occurs due to increase in the magnet temperature by heat generation, the output torque of the AC rotary machine reduces.
In order to cope with the above problem, the following control apparatus for an AC rotary machine is disclosed. That is, the control apparatus for an AC rotary machine performs torque control for the AC rotary machine over a wide rotation rate region from zero to a high speed while appropriately switching the above-described drive methods of the power converter (sine wave PWM control method or square wave drive method) in accordance with the operation condition of the AC rotary machine (typically, the induced voltage, torque, and rotation rate of the AC rotary machine), and performs feedback control by estimating the output torque of the AC rotary machine in order to suppress torque variation (for example, see Patent Document 1 shown below).
According to Patent Document 1, the control method for voltage conversion in the power converter is selectively set in accordance with the operation condition of the AC rotary machine. That is, if control method selection means selects a first control method to apply square wave voltage to the AC rotary machine, the torque control is performed by feedback control adjusting the phase of the square wave voltage in accordance with the torque deviation from a torque instruction value in the torque control. In addition, if the control method selection means selects a second control method to control the voltage applied to the AC rotary machine in accordance with the pulse width modulation method using vector control, the torque control is performed by feedback control for the current of the AC rotary machine.
Thus, when the second control method is selected, feedback control for the current of the AC rotary machine is performed including the same feedback control as in the first control method which is performed in accordance with the torque deviation. Therefore, motor current control can be performed so as to compensate the variation in the torque characteristic of the AC rotary machine which depends on temperature variation or the like. As a result, it becomes possible to prevent occurrence of the torque variation due to magnet temperature variation or the like without particularly providing a temperature sensor or the like. In addition, since both the first and second control methods perform the feedback control in accordance with the torque deviation, it is possible to prevent occurrence of the torque variation upon switching between the control methods.